Patterning mechanism for circular knitting machines

ABSTRACT

A patterning mechanism for a circular knitting machine having a stack or series of rotary discs with peripheral formations which may be present or absent according to a predetermined pattern. When present, they are co-operable with a single patterning butt on each of a series of presser elements which cooperate with needles to be controlled, the presser elements each having a series of height selection butts by means of which the presser elements are raisable and lowerable so that the patterning butts of the presser elements are co-operable with selected discs of the stack or series. The height selection butts co-operate with upper and lower supporting edges on a guide ring to maintain the presser elements at preset levels between successive passages through one or more level changing stations. A presser element lowering cam is located at each level-changing station. When the pressure element lowering cam is placed in the path of the butts travelling clear of and above the upper supporting edge it brings them into engagement with surfaces on the upper and lower supporting edges of the guide ring. Height selection butts of presser elements which are not to change level at a station pass through a guide track insertable between the upper and lower supporting edges of the guide ring.

United States Patent Farmer et al.

[ Apr. 23, 1974 PATTERNING MECHANISM FOR CIRCULAR KNITTING MACHINES [75] Inventors: Ernest Leonard Farmer; Dennis William Whitmore, both of Leicester, England [73] Assignee: Wildt Mellor Bromley Limited,

. Leicester, England [22] Filed: Mar. 12, 197i 211 Appl. N0.: 123,592

[30] Foreign Application Priority Data Mar. 24, 1970 Great Britain 14244/70 [52 us. cl.-... 66/50 B, 66/57 [51] Int. D04b 15/74 [58] Field of Search 66/50 R, 50 B, 25, 36 A,

' [56] References Cited ,UNITED STATES PATENTS 3,64l,786 2/l972 Burdettet aI. 66/50B 2,193,872 3/1940 Jackson et al... 66/50 3,315,494 4/1967 Farmer... 66/50 R FOREIGN PATENTS OR APPLICATIONS l,l l3,296 5/1968 Great Britain 66/50 B 534,824 10/1955 Italy ..66/5OR Primary Examiner-Wm. Carter Reynolds A patterning mechanism for a circular knitting machine having a stack or series of rotary discs with peripheral formations which may be present or absent according to a predetermined pattern. When present,

they are co-operable with a single patterning butt on each of a series of presser elements which cooperate with needles to be controlled, the presser elements each having a series of height selection butts by means of which the presser elements are raisable and lowerable so that the patterning butts of the presser elements are co-operable with selected discs of the stack or series. The height selection butts co-operate with upper and lower 'supporting edges on a guide ring to maintain the presser elements at presetlevels between successive passages through one or 'morelevel changing stations. A presser element lowering cam is located at each level-changing station. When the pressure element lowering cam is placed in the path of the butts travelling clear of and above the upper supporting edge it brings them into engagement with surfaces on the upper and lower supporting edges of the guide ring; l-leight selection butts of presser elements which are not to change level at a station pass through a guide track insertable between the upper and lower supporting edges of the guide ring.

'5 Claims, 5 Drawing Figures sum 10F 3 :ATENTED APR 2 m4 INVENTOR RD FABg/lERjtal ATTORNEY L 1 w w w E c n 3 5 2 56 \\MM\ FIGS.

ERNEST LEONA BY 2 Y////IL\\\\A\ \\\\1 PATEMTEDAPR IHM SHEET 2 BF 3 INVENTOR ERNEST LEONARD J 2. 2%;

ATTORNEY PATENTED APR 2 3 19m SHEET 3 [IF 3 INVENTOR ERNEST LEONARD BY FARNER ctql ATTO.RNEY

PATTERNING MECHANISM FOR CIRCULAR KNITTING MACHINES This invention relates to patterning mechanisms for circular knitting machines, and has particular reference to patterning mechanisms of the type comprising a stack or series of rotary discs or other rows of peripheral formations, having peripheral format-ions present or absent according to a predetermined pattern and cooperable with a single patterning butt on each of a series of presser elements associated with needles to be controlled, the presser elements each having a series of height selection butts by means of which the presser elements are raisable and lowerable so that the patterning butts of the presser elements are cooperable with selected discs or rows of the said stack or series.

Patterning mechanisms of this type are described and claimed in our United Kingdom Patent Specification 1029373 and U.S. Pat. No. 3,315,494 issued on Apr. 25, I967 to E. L. Farmer. One or more stations for raising and lowering the presser elements are provided so that the presser elements may be moved'up and, down once (or more times) per revolution of the needle cylinder.

The station includes selectively usable cams for raising and lowering thepressure elements, and the pressure elements are maintained at the selected location by a guide ring cooperable with the height selection butts. In order to provide positive support of the presser elements, the guide ring is arranged to cooperate with two height selection butts of each presser element and in the particular arrangement described, it has a channel section so as to provide two supporting edges, each having an upwardly facing surface and a downwardly facing surface. The pitching and dimensions of the height selection butts and'the supporting edges are so chosen that two modes of positive support are available. In a first mode of support, two adjacent height selection butts are. engaged within the guide ring, with the upper butt cooperating with the downwardly facing surface of the upper supporting edge and the lower butt cooperating with the upwardly facing surface of the lower supporting'edge. In the second mode of support, one height selection butt is free between the supporting edges of the guide ring and the upwardly adjacent butt cooperates with the upwardly facing surface of theupper supporting edge, and a downwardly adjacent butt cooperates with the downwardly facing surface of the lower supporting edge.

United Kingdom Patent Specification No. 1029373 and US. Pat. No. 3,315,494 issued on Apr. 25, 1967 to E. L. Farmer describe a mode of changingthe position of the height selection butts, and hence of the presser elements relative to the rotary discs, which involves the use of at raising cam. and a lowering earn which are selectively brought into the paths of height selection butts having specified relationships with the guide ring. The guide ring is interrupted in the vicinity of the cams, i.e. at the raising and lowering station, to allow the height selection butts to change position relative to the supporting edges. The raising cam normally engages the butt next below the butt in engagement with the lower supporting edge in the first mode of support and carries it to the position of engagement with the upwardly facing surface of the lower supporting edge, thus shifting the presser element up by one butt pitch. The lowering cam normally engages the butt on the upwardly facing surface of the upper supporting edge in the second mode of support and carries it down to the free position midway between the supporting edges, thus lowering the presser element by one butt pitch. In the case of an upward movement from the second mode of support, or a downward movement from the first mode of support, the height selection butt engaged by the cam is originally halfway along the selected movement and the raising or lowering is then by one half of one butt pitch.

In this arrangement the interruptions in the supporting edges of the guide ring have to be quite long, as the lowering cams must pass through the upper supporting edge surface.

Also, with this arrangement of the lowering cams, the raising and lowering cams are spaced apart by only a small distance and it is not easily practicable to provide a straight through support for guiding the height selection butts on a level path through the interruption of the guide ring if neither raising nor lowering is required, but merely a repeat of the previous level.

Further in the arrangement described in the United Kingdon Patent Specification 1029373 and US. Pat. No. 3,315,494 issued on Apr. 25, 1967 to E. L. Farmer the lowest position of the presser element is defined with the topmost height selection butt midway between the supporting edges so that other means must be provided to prevent the presserelement falling under gravity from this position, if this position is to be used in practice. I

The present invention consists in a patterning mechanism of the type described wherein the height selection butts cooperate with the upper and lower supporting edges on a guide ring to maintain the presser elements at preset levels between successive passages through one or more level changing stations, and wherein a presser element lowering cam at the or each levelchanging station is adapted to be placed in the path of the butts travelling clear of and above the upper supporting edge to bring them into engagement with one of the surfaces thereof, preferably the upper surface. with the presser element raising cam operating as described above, there is then-a distinct vertical spacing between the two cams'which can be used for a short length of guide track to guide the height selection butts through the level changing station when no levelchange is required.

The-raising cam, the lowering cam and the said short length of track are preferably conjointly controlled so that one and only one of them is in operative position in the level changing station at any one time.

The invention will be further described with reference to the accompanying drawings, which show a preferred embodiment, given by way of example only, and not byway of limitation.

In the drawings:

FIG. 1 is a vertical section of part of a circular knitting machine showing a stack or series of rotary discs cooperating with the presser;

FIG. 2 is a side elevation partly in vertical section, of part ofa knitting machine taken at a level changing station;

FIG. 3 is an elevation of the arrow III of FIG. 2 showing the level changing cams and associated parts;

FIG. 4 is a section on the line IV-IV of FIG. 2 showing part of the interlocking mechanism; and

FIG. is an end elevation of the structure of FIG. 2.

FIG. 1 is a sectional view, taken at a selection station, of a knitting machine which is generally of the type described in our United Kingdom Patent Specification 1029373 and US. Pat. No. 3,315,494 issued on Apr. 25, 1967 to E. L. Farmer. Only those parts of the machine as are necessary for the understanding of the selection operation are shown, and it will be appreciated that the drawing is to a certain extent diagrammatic.

A rotary needle cylinder 1 has in the outer surface thereof a plurality of needle tricks 2, each of which carries a latch type needle 3. Each needle 3 is supported on a needle operating jack 5 operating in the needle trick 2. Each jack has a downwardly extending springy extension 5a terminating in a butt 6 which is adapted to cooperate with a cam, shown at 7, to lift the jack 5 and needle 3 for a knitting operation. The springy nature of the extension 5a is such that the butt 6 is normally urged out of the needle trick 2 so that its path is over the cam 7, but a presser 8 is associated with needle 3 and jack 5 whereby the jack may be depressed into its trick so that the butt 6 passes behind the cam 7 and the needle does not therefore rise to knitting position.

Each presser 8 on the fine gauge knitting machine illustrated is provided with a selection butt 9 and or 9', for cooperation with peripheral formations 10a formed on rotary pattern elements such as discs 10 mounted in pairs in a stack at the selecting station. The upper disc of each pair is arranged at such a level as to have its peripheral formations cooperating with the butts 9 on alternate pressers 8, while the lower disc cooperates with the butts 9 on the intervening pressers 8. The peripheral formations 10a, or the locations for them where they are omitted, on the discs 10 ofa pair are staggered in relation to each other so that one disc of each pair operates on alternate needles, while the other disc operates on the intervening needles. Such an arrangement is necessary where the needles are of fairly close pitch, but where the needles are coarsely pitched, then the discs may each be made to operate on each presser and the use of the two levels of butts becomes unnecessary, and they may be replaced by butts at a single level. lt will also be understood that in the case of exceptionally fine pitching, it may be desirable to have the discs in groups of three or even more.

The stack of discs 10 is mounted on a shaft 11 with spacers 12 between them, and the shaft 11 is driven in synchronism with the needle cylinder 1, by means ofa gear 13 mounted on the cylinder 1 meshing with a gear 14 mounted on the shaft 11.

The butts 9, 9 cooperate with selected pairs of the discs 10 depending on the level of the pressers 8, and this level is controlled by a series of height selection butts 15 provided on the pressers and cooperating with a guide ring or track 16 which maintains them at their selected height. The actual level is determined at one or more level changing stations situated around the periphery of the needle cylinder 1, whereat the butts 15 are acted on by cams to raise or lower the level of the presser 8, and hence of the butt 9 or 9' cooperating with the discs 10.

Where the disc 10 has a peripheral formation 10a which bears on the butt portion 9 or 9', then the presser 8 and jack 5 are depressed into the trick and the butt 6 misses the cam 7 and passes behind it, thereby causing the needle to miss rather than knit. lf the appropriate part of the disc 10 is not provided with a peripheral formation, then the butt 9 or 9' is not engaged and the presser and jack are not pressed into the trick, so that the butt 6 rides up the cam 7, and the jack 5 lifts the needle into the knitting position.

The mechanism is very similar to that described in the United Kingdom Patent Specification 1029373 and U.S. Pat. No. 3,315,494 issued on Apr. 25, 1967 to E. L. Farmer, and so far as FIG. 1 goes, the only difference is that whereas in the United kingdom Patent Specification 1029373 and U .S. Pat. No. 3,315,494 issued on Apr. 25, 1967 to E. L. Farmer, there are illustrated eighteen pairs of discs 10 and nine height selection butts 15 on each presser, i.e. one half of the numbers of pairs of discs, in the present drawing there are shown 12 pairs of discs and eight height selection butts 15 on each presser, i.e. two more than half the number of discs.

The dimensioning of the track 16 and the dimensioning and pitching of the butts 15 are similar to those described in the United Kingdom Patent Specification 1029373 and US. Pat. No. 3,315,494 issued on Apr. 25, 1967 to E. L. Farmer, so that the butt 15 may be supported by the track in the two types of position described and illustrated in these Patent Specifications. As illustrated in FlG. 1 of the present drawings, two butts are contained within the track 16, which is the position adopted by the pressers at the conclusion of the raising action at the height selection station, and each complete raising action i.e. from this position to the next similar position upwards, lifts the butts 9 or 9 of the pressers from the level of one pair of discs to the next butt one level upwards. The intervening pairs of discs are in cooperation with butts 9 or 9 when the alternate position is adopted, in which one butt 15 is located within the track, and the adjacent butts above and below it are located immediately outside the track so as to embrace it. This is the position adopted by the pressers on the conclusion of a lowering action at the level selection station.

FIGS. 2 to 5 illustrate a level selection station. As in the United Kingdom Specification 1029373 and US. Pat. No. 3,315,494 issued on Apr. 25, 1967 to E. L. Farmer, the lifting and lowering of the pressers is achieved by alternatively operable cams 17 and 18 which can be brought into the path of appropriately located butts 15 to lift or lower the pressers respectively. The cams l7 and 18 are mounted in a housing 19 which carries extension pieces 16a and 16b for the track 16 for cooperation with the cams l7 and 18. The housing 19 also carries a guide track 20 which enables the pressers 8 to be passed through the level selection station at a constant level without any risk of their butts falling through the vertical gap in the track provided between the track extension pieces 16a and 16b.

The operation of the cam 17, when this is in the operative forward position is to entrain the butts 15 on the pressers 8 on the position next below the position of the lower of the two butts illustrated in the track 16 in FIG. 1 and to carry them into this latter position. In a normal lifting operation the butt which had hitherto occupied this position then becomes the upper of the two butts within the track 16. However, should the preceding change of levels have been in a downward operation, then the starting position will be slightly different and the operation of the cam 17 will be to lift the pressers 8 by one half of one butt pitch, rather than a complete butt pitch.

The operation of the cam 18 is to entrain a butt above and clear of the top of the track 16 and to lower it to a position wherein it rides on the upper surface of the upper edge of the track 16. The butt which had hitherto been riding in this position then takes up a position intermeidate the two edges of the track 16 and the butt hitherto in that position takes up a position immediately below the lower surface of the lower edge of the track 16. This covers the case of the full butt pitch movement which is characteristic of a lowering action which follows a lowering action. However, if the previous change of level has been a raising action, then the level change will again be by one haf butt pitch, i.e. by one pair of discs rather than by two. The guide track has the function of guiding a pair of butts within the path defined by the upper and lower supporting edges of the guide, or a single butt in an intermediate position within the track, without level change, and its action needs no further explanation.

The selection of the cams 17, 18 and the guide 20 is by means of ajselection mechanism similar to that described in United Kingdom Patent Specification 1029373 and US Pat. No. 3,315,494 issued on Apr. 25, i967 to E. L. Farmer, extended to cover the three possibilities involved. This mechanism is illustrated generally at 2 1, and will not be further described in detail.

The cam 18 is mounted on a slide 22, the cam 17 on a slide 23 and the guide 20 on a slide 24. The slides 22, 23 and 24 eachhave an adjusting screw 22a, 23a and 24a cooperating with a bell crank 22b, 23b and 24b operated by the appropriate parts of the selection mechanism 21. These bell cranks are spring returned, and are adapted to be held in position by a catch 25 which holds the operated bell-crank in position against the appropriate head of the appropriate slide until subsequent operation of the mechanism 21 selects a different bell crank to release the catch 25 and the previously operated bell crank.

This catch mechanism forms the subject of our copending application Ser. No. 123,591 filed March I2, 1971 and entitled Improvements in or relating to patterning mechanism for circular knitting machines.

FIGS. 2 and 4 show that the slides 22 and 23 each i have a pin 26 and 27 respectively co-operating with a slotted disc 28 mounted within the housing 19 to ensure that the forward operation of one of the slides 22 and 23 ensures a conjoint reverse operation of the other of these two slides. Each of these two slides has a shoulder 30 and 31 cooperating with a pin 32 mounted in the slide 24. This ensures that forward movement of the slide 24, to bring the guide 20 into operative position causes partial forward movement of -whichever of the slides, 22 and 23 has been in its rewithdraw the slide 24 and the guide 20 to inoperative position.

As described in United Kingdom Patent Specification 1029373 and US. Pat. No. 3,315,494 issued on Apr. 25, 1967 to E. L. Farmer, there is normally provided a substantial space between needle tricks at one location on the needle cylinder, and while this gap is passing the height selection station, the changeover of height selection may be achieved.

When the selector mechanism operates to select a particular one of the slides 22, 23 or 24, the appropriate. bell crank is brought forward against its return spring and releases the latch 25 to allow any previousy operated bell crank to return to its operative position under the influence of the return spring. The selected bell crank continues forward and depresses the appropriate slide, and the interlock arrangements between them ensure that the remaining slides are withdrawn from the path of the butts. If the slide 22 is selected, then the cam 18 is put into the operative position and the pressers are each brought .to the next lower position on the descending scale as they pass the cam 18 at the level selection station. Similarly, if the cam 17 is selected, the pressers are each moved to the next upward type position, i.e. the position illustrated in FIG. 1 with two butts between the edges of the track 16, until the cam 17 is retracted. if the guide 20 is inthe operative position then the pressers remain at constant position until this slide is retracted and one of the cams l7 0 18 is brought into operation.

Various modification may be made within the scope of the invention.

We claim: v 1. ln a patterningmechanism for a circular knitting machine with a rotary needle cylinder, in which the patterning mechanism is of .the type comprising a rotary pattern element havinga series of rows of peripheral formations which are present or absent at given positionsaccording to a predetermined pattern, the peripheral formations cooperating with a single patterning butt on each of a series of presser elements associated with needles to be controlled, each presser element having a series of height selection. butts by means of which the presser elements are raisable and lowerable at at least one level changing station so that the patterning butts of the presser elements are cooperable with selected rows of said series of presser elements, a peripheral formations lowering cam and a presser element raising cam at said level changing station, a guide ring extending around the needle cylinder and having upper and lower supporting edges and a vertical gap interupting the upper. and lower supporting edges, each of the supporting edges having upper and lower surfaces cooperating with the height selection butts to maintain the presser elements at pre-set levels between successive passages through said at least one level selecting station: the improvement that said at least one level changing station includes a short length of guide track disposed between the upper and lower supporting edges of the guide ringat the vertical gap, to guide the height selection butts through the station when no level change is required and to prevent the pressers from falling through the gap and said presser element lowering cam at each level selecting station being adapted to be placedin the path of the height selection butts at a level clear of and immediately above the upper supporting edge to bring them into engagement with one of the surfaces of the upper supporting edge of said guide ring, and wherein the guide track guides either a pair of presser element height selection butts within the path defined by the upper and lower supporting edges without level change or a single presser elements height selection butt in an intermediate position within the guide track without level change.

2. A patterning mechanism as claimed in claim 1, wherein each presser element lowering cam is adapted to bring the butts into engagement with the upper surface of the upper supporting edge.

3. A patterning mechanism as claimed in claim 1, which further includes means for conjointly controlling the raising cam, the lowering cam and the short length of track so that one and only one of these is in operative position at the level changing station at any one time.

4. In a patterning mechanism for a circular knitting machine with a rotary needle cylinder in which the-patterning mechanism is of the type comprising a rotary pattern element having a series of rows of peripheral formations which are present or absent at given positions according to a predetermined pattern, the peripheral formations cooperating with a single patterning butt on each of a series of presser elements associated with needles to be controlled, each presser element having a series of height selection butts by means of which the presser elements are raisable and lowerable at at least one level changing station so that the patterning butts of the presser elements are cooperable with selected rows of said series of peripheral formations, a presser element lowering cam and a presser element raising cam at said level changing station, a guide ring extending around the needle cylinder and having upper and lower supporting edges and a vertical gap interupting the upper and lower supporting edges, each of the supporting edges having upper and lower surfaces cooperating with the height selection butts to maintain the presser elements at pre-set levels between successive passages through said at least one level selecting station: the improvement that said at least one level changing station includes a short length of guide track disposed between the upper and lower supporting edges of the guide ring at the vertical gap'to guide the height selection butts through the station when no level change is required and to prevent the presser elements from falling through the gap, said presser element lowering cam at each level selecting station being adapted to be placed in the path of the height selection butts at a level clear of and immediately above the upper supporting edge to bring them into engagement with one of the surfaces of the upper supporting edge of said guide ring, separate slides on which the raising cam, the lowering cam and the short length of track are mounted, individual operating means for the slides and interlock means for ensuring that operation of any one slide to the operative position ensures retraction of any other slide at the level changing station from its operative position, and wherein the guide track guides either a pair of presser element height selection butts within the path defined by'the upper and lower supporting edges without level change or a single presser element height selection butt in an intermediate position within the guide track without level change.

5. A patterning mechanism as claimed in claim 4, in which the slides for the lifting cam and the lowering cam are provided with an interlock mechanism ensuring equal and opposite movements of the two slides, and also with abutments cooperating with abutments on the slide for the short length of track whereby advance of the slide for the short length of track will entrain one of the cam slides directly for a short forward movement sufficient to bring the short length of the track to operative position but insufficient to bring the cam to operative position, while also retracting the other cam slide through the interlock mechanism. 

1. In a patterning mechanism for a circular knitting machine with a rotary needle cylinder, in which the patterning mechanism is of the type comprising a rotary pattern element having a series of rows of peripheral formations which are present or absent at given positions according to a predetermined pattern, the peripheral formations cooperating with a single patterning butt on each of a series of presser elements associated with needles to be controlled, each presser element having a series of height selection butts by means of which the presser elements are raisable and lowerable at at least one level changing station so that the patterning butts of the presser elements are cooperable with selected rows of said series of presser elements, a peripheral formations lowering cam and a presser element raising cam at said level changing station, a guide ring extending around the needle cylinder and having upper and lower supporting edges and a vertical gap interupting the upper and lower supporting edges, each of the supporting edges having upper and lower surfaces cooperating with the height selection butts to maintain the presser elements at pre-set levels between successive passages through said at least one level selecting station: the improvement that said at least one level changing station includes a short length of guide track disposed between the upper and lower supporting edges of the guide ring at the vertical gap, to guide the height selection butts through the station when no level change is required and to prevent the pressers from falling through the gap and said presser element lowering cam at each level selecting station being adapted to be placed in the path of the height selection butts at a level clear of and immediately above the upper supporting edge to bring them into engagement with one of the surfaces of the upper supporting edge of said guide ring, and wherein the guide track guides either a pair of presser element height selection butts within the path defined by the upper and lower supporting edges without level change or a single presser elements height selection butt in an intermediate position within the guide track without level change.
 2. A patterning mechanism as claimed in claim 1, wherein each presser element lowering cam is adapted to bring the butts into engagement with the upper surface of the upper supporting edge.
 3. A patterning mechanism as claimed in claim 1, which further includes means for conjointly controlling the raising cam, the lowering cam and the short length of track so that one and only one of these is in operative position at the level changing station at any one time.
 4. In a patterning mechanism for a circular knitting machine with a rotary needle cylinder in which the patterning mechanism is of the type comprising a rotary pattern element having a series of rows of peripheral formations which are present or absent at given positions according to a predetermined pattern, the peripheral formations cooperating with a single patterning butt on each of a series of presser elements associated with needles to be controlled, each presser element having a series of height selection butts by means of which the presser elements are raisable and lowerable at at least one level changing station so that the patterning butts of the presser elements are cooperable with selected rows of said series of peripheral formations, a presser element lowering cam and a presser element raising cam at said level changing station, a guide ring extending around the needle cylinder and having upper and lower supporting edges and a vertical gap interupting the upper and lower supporting edges, each of the supporting edges having upper and lower surfaces cooperating with the height selection butts to maintain the presser elements at pre-set levels between successive passages through said at least one level selecting station: the improvement that said at least one level changing station includes a short length of guide track disposed between the upper and lower supporting edges of the guide ring at the vertical gap to guide the height selection butts through the station when no level change is required and to prevent the presser elements from falling through the gap, said presser element lowering cam at each level selecting station being adapted to be placed in the path of the height selection butts at a level clear of and immediately above the upper supporting edge to bring them into engagement with one of the surfaces of the upper supporting edge of said guide ring, separate slides on which the raising cam, the lowering cam and the short length of track are mounted, individual operating means for the slides and interlock means for ensuring that operation of any one slide to the operative position ensures retraction of any other slide at the level changing station from its operative position, and wherein the guide track guides either a pair of presser element height selection butts within the path defined by the upper and lower supporting edges without level change or a single presser element height selection butt in an intermediate position within the guide track without level change.
 5. A patterning mechanism as claimed in claim 4, in which the slides for the lifting cam and the lowering cam are provided with an interlock mechanism ensuring equal and opposite movements of the two slides, and also with abutments cooperating with abutments on the slide for the short length of track whereby advance of the slide for the short length of track will entrain one of the cam slides directly for a short forward movement sufficient to bring the short length of the track to operative position but insufficient to bring the cam to operative position, while also retracting the other cam slide through the interlock mechanism. 